Project Summary/Abstract E-cigarette use is increasing rapidly in the United States, especially amongst youth, underscoring the vital need to improve understanding of its health risks. Relevant data could inform policy, guide public health and clinical intervention efforts, and inform individuals who might use or who are using this product. In this proposal, we describe research that will significantly enhance our understanding of the health effects of E-cig use by relating the acute and long-term use of E-cigs and conventional cigarettes (?products?) to well- validated cardiovascular and pulmonary disease biomarkers. We will enroll 4 different ?use-groups? of participants (n=440): exclusive E-cig users (n=110), exclusive cigarette smokers (n=110), dual product users (who both smoke and vape: n=110), and never smokers (n=110). These groups reflect the primary decisions that individuals can make regarding their future tobacco use: to continue to smoke cigarettes, to switch to E- cigs, to use both cigarettes and E-cigs, or to not use products. It is essential that smokers and health care providers have accurate information on the health effect of these choices. Product use will be related to well-validated biomarkers that accurately and reproducibly reflect mechanisms, injury, and future risks related to cardiovascular or pulmonary disease. Biomarkers will be related to (1) acute product use in the laboratory (exposure challenges), (2) lifetime history of product use, and/or (3) real-time measures of product use in participants' daily lives. The primary cardiovascular biomarkers are brachial artery flow-mediated dilation (a measure of endothelial function) and carotid intima-media thickness, a measure of subclinical arterial injury and atherosclerosis. The primary pulmonary disease biomarkers will be measures of lung volumes and flow rates (predicted FEV1, FVC, FEV1/FVC) obtained by spirometry. We also will perform treadmill exercise stress testing (to assess aerobic fitness), electrocardiography (to measure heart rate and its variability) and measure blood pressure, lipids, HgbA1c, and inflammation/oxidation markers (leukocyte count, C-reactive protein, urinary F2 isoprostanes) and exhaled nitric oxide. We will show how product use-groups differ in response to (1) acute product use and (2) long-term use regarding cardiovascular and pulmonary biomarkers. We also will determine how history of product use is related to biomarker status. The proposed research will yield vital and comprehensive data regarding product use, subclinical arterial injury, atherosclerosis burden, arterial and pulmonary function, cardiac and aerobic fitness, cardiac autonomic dysregulation, systemic and pulmonary inflammation, and oxidative stress, as well as other key outcomes. These data will serve as a foundation for future longitudinal investigations of E-cig health effects and will inform public policy decisions, clinical interventions, and patient guidance regarding E-cigarettes.